A silencer which operates satisfactorily at a low speed of the engine, when the flow rate of the gases is comparatively small and pulsations in the gas flow are relatively large, does not operate at maximum efficiency at the time the speed of the engine is increased, when the flow rate of the gases exhausting from the engine becomes comparatively large, and the magnitude of the pulsations in the gas flow become relatively smaller.
Various proposals have been made to increase the operating efficiency of such silencers over the entire range of engine speeds, but, those attempts have largely involved a compromise between the various parameters involved, in that they employ structures which are fixed relatively to each other, and which are thus incapable of varying in position in dependence on the engine speed and the characteristics of the exhaust gas flow therefrom.
It has been proposed to provide a silencer in which a main silencer is movable axially with respect to the inlet thereto in order that the axial length of the inlet conduit may be varied in order to adjust the characteristics of the silencer to the varying parameters of the engine exhaust. Such a structure is, however, cumbersome and difficult to support on a vehicle such as a motorcycle, and, further problems are encountered in accommodating the varying length of the silencer as it moves between an extended and a retracted position.